1. Field of the Invention
This invention pertains generally to displays comprising an array of display elements and more particularly to a method and system wherein array address information is encoded within each display element wherein the elements may be controlled utilizing simplified driver circuits.
2. Description of the Background Art
Display arrays utilize a collection of elements which are controlled in concert with one another for displaying text or graphics. A scrolling LED advertising panel is typical of such a display array. These displays are increasingly utilized both outdoor and indoor for conveying information and advertising. The display elements within these arrays are typically LEDs which are usually provided as single color, dual color, or multicolor, such as red/green/blue (RGB). Large displays may encompass tens of thousands of elements for a large area display or marquee. The use of incandescent bulbs in signs is also prevalent within certain forms of signage, however, as the cost of LEDS decreases and the available intensity increases, fewer signs are utilizing incandescent lighting elements. Although display arrays have become increasingly important, their basic designs has not significantly changed since the 1970s.
In order to appreciate the beneficial aspects of the present invention, it is necessary to generally understand the design and construction of display arrays as they are currently being designed and produced. Elements of a display array are generally arranged in rectangular arrays with rows and columns. In systems with only a few discrete display elements, each element may be individually turned on and off by a controller in a direct (non-multiplexed) operation. However, display multiplexing, as generally shown in FIG. 1, was introduced to overcome the difficulty with providing individual signals for each element of a large array. Basically, in a multiplexed display each display element is connected across a row and a column, such that any element may be enabled, or lit up, by providing power on a column while pulling one of the rows to ground. By quickly scanning across the rows and columns each element can be individually driven for a small duty cycle. Multiplexing reduces the number of control lines necessary but results in a commensurate loss of maximum output intensity. It will be appreciated that each display element may only be driven for a small percentage of the time, depending on the depth of multiplexing utilized, and the achievable display intensity is therefore reduced. In the array of FIG. 1 it will be appreciated that power to one column may be applied wherein current sinking by the row driver activates any LEDs in that column, wherein each LED can be activated for a maximum of 1/6  of the total time as there are a total of six columns which are being driven. In displays requiring greater intensity, such as outdoor displays, the depth of multiplexing must be reduced and many displays utilize drivers for each display element.
A typical multiplexed small to medium sized display array comprises a housing, a backplane, driver chips distributed on the backplane, one or more controller chips for orchestrating the driver chips, a main processor, a power supply, and of course the display elements themselves. Considering a small two line display of 16 rows and 250 columns it will be appreciated that traces must be routed on the backplane to each element within the 16 rows and 250 columns. If multi-color elements are being used, then the two or three sets of rows and columns may be required for each element. On an array of even this miniature size, it would not be possible to multiplex the whole display with only one LED on at a time as each LED could be active a maximum of 1/4000th of the time. Therefore, separate drivers are typically provided for each column and the 16 vertical rows would then be multiplexed so that the elements can be active up to 1/16th of the overall time which would define maximum element brightness. Signal traces and drivers are required for each of the 250 columns and the 16 rows, and that the controller software must accommodate the structure of the multiplexing which is different for each display. Larger displays are generally composed of panels which act as separate displays that each have a controller and a set of row and columns. Each of these separate panels is integrated to one another by another level of driver circuitry. Very large displays can appear reminiscent of an antiquated mainframe computer, replete with complex racks of driver cards, and they are extremely expensive to produce and maintain. When faulty driver circuits occur, entire rows or columns of the display are affected and a service person is often required to locate a suitable replacement (often difficult as the driver circuits change so often) and then remove the surface mounted integrated circuits, with perhaps 100-200 leads, from the display array and solder in the new device.
Manufacture of display arrays is also complex and expensive. In order to fabricate a multiplexed display of a different/custom size a completely new design is required to suit the characteristics of the display. The design requires not only the design of a new backplane, but of all the drive electronics, as the row and column drivers are integrated for the specific number of rows and columns, and to one another, and also for the particular type and configuration of display element being driven. Often each display type and size utilizes its own proprietary control software to properly control the custom array of driver circuits whose operation is to be coordinated. For example, even a small change such as changing from 16 to 18 rows in the previous example would require a complete redesign of the display which would obviously be extremely expensive. Furthermore, it will be understood that large backplanes are expensive to fabricate and populate with distributed driver chips. Therefore, the costs are high even for a production run of displays, such as the 16×250 element array.
It is apparent that the display arrays pose numerous unresolved design problems with regard to multiplexed brightness, production cost, engineering cost, the capability to customize, the reliability, and the serviceability. Therefore, a need exists for a method and apparatus which would provide for controlling large arrays of display elements without the present “row and column” complexities and limitations.
The universal scanning method and system for driving optical elements in accordance with the present invention satisfies that need, as well as others, and overcomes deficiencies in previously known display array drive techniques.